Identify the conjugate acid-base pair from the following equilibrium reaction.
$HSO_{3(aq)}^{-} + H_3O_{(aq)}^{+} \rightleftharpoons H_2SO_3 + H_2O$

• A
  $H_2SO_3$ and $HSO_3^{-}$
• B
  $HSO_3^{-}$ and $H_3O^{+}$
• C
  $H_2SO_3$ and $H_2O$
• D
  $H_3O^{+}$ and $H_2SO_3$